1. Field of the Invention
The present invention relates to techniques for providing treatment therapy to neural tissue, and more particularly relates to techniques for selectively delivering treatment therapy to neural tissue located within a volume of the brain, spinal cord, or peripheral nerve.
2. Description of Related Art
Electrical stimulation techniques have become increasingly popular for treatment of pain and various neurological disorders. Typically, an electrical lead having one or more electrodes is implanted near a specific site in the brain or spinal cord of a patient. The lead is coupled to a signal generator which delivers electrical energy through the electrodes to nearby neurons and neural tissue. The electrical energy delivered through the electrodes creates an electrical field causing excitation of the nearby neurons to directly or indirectly treat the pain or neurological disorder.
Presently, only highly skilled and experienced practitioners are able to position a stimulation lead in such a way that the desired volume of brain tissue is influenced and desired results are obtained over time with minimal side effects. It requires much time and effort to focus the stimulation on the population of nerve cells subserving the appropriate function in the desired body region during surgery. These leads cannot be moved by the physician without requiring a second surgery.
A major practical problem with these systems is that the response of the nervous system may change in time. For example, when treating pain even if paresthesia covers the areas in pain perfectly during surgery, the required paresthesia pattern often changes later due to lead migration, histological changes (such as the growth of connective tissue around the stimulation electrode), neural plasticity or disease progression. As a result, the electrical energy is directed to stimulate undesired portions of the brain or spinal cord. Redirecting paresthesia without requiring a second surgery is therefore highly desirable. With present single channel, linear electrode array approaches, however, it is difficult to redirect stimulation effects afterwards, even though limited readjustments can be made by selecting a different contact combination, pulse rate, pulse width or voltage. These problems are found not only with spinal cord stimulation (SCS), but also with peripheral nerve stimulation (PNS), depth brain stimulation (DBS), cortical stimulation and also muscle or cardiac stimulation.
In the case of DBS where an electrical lead is implanted within the brain, it is particularly critical that the lead be properly positioned. If the lead is not properly positioned and needs to be moved, it must be removed and re-inserted thereby increasing the risk of bleeding and damage to the neuropile. It is therefore desirable to place the lead within the brain in one attempt and avoid subsequent movement or repositioning of the lead.
Recent advances in this technology have allowed the treating physician or the patient to steer the electrical energy delivered by the electrode once it has been implanted within the patient. For example, U.S. Pat. No. 5,713,922 entitled xe2x80x9cTechniques for Adjusting the Locus of Excitation of Neural Tissue in the Spinal Cord or Brain,xe2x80x9d issued on Feb. 3, 1998 to and assigned to Medtronic, Inc. discloses one such example of a system for steering electrical energy. Other techniques are disclosed in application Ser. Nos. 08/814,432 (filed Mar. 10, 1997) now U.S. Pat. No. 5,925,070 and 09/024,162 (filed Feb. 17, 1998) now U.S. Pat. No. 6,035,480. Changing the electric field distribution changes the distribution of neurons recruited during a stimulus output thus provides the treating physician or the patient the opportunity to alter the physiological response to the stimulation. The steerability of the electric field allows the user to selectively activate different groups of nerve cells without physically moving the electrode.
These steering techniques, however, are limited to primarily two-dimensional steering since the electrodes are positioned in a linear or planar configuration. In the case of deep brain stimulation (DBS), the stimulation treatment requires stimulation of a volume of neural tissue. Since the exact location of the desired tissue is unknown, it is desirable to steer the electrical field in more than just two-dimensional space.
Another problem with DBS is that the insertion of electrical leads within the brain presents risks of bleeding or damage to the brain tissue. Where multiple leads are inserted within the brain, this risk also multiplies. Often during placement of a lead within the brain, the lead is not placed in the desired location. The lead must be removed and re-inserted into the brain. Each re-insertion of the lead poses additional risk of injury.
Accordingly, there remains a need in the art to provide a two- or three-dimensional steerable electrical stimulation device that may be implanted within the brain or spinal cord parenchyma that requires minimal adjustment of the lead position.
As explained in more detail below, the present invention overcomes the above-noted and other shortcomings of prior techniques for electrical stimulation of the brain, spinal cord parenchyma and peripheral nerve. The present invention provides a technique for insertion of electrode leads that require minimal adjustment once the lead has been inserted. Additionally, the present invention enables the user to selectively stimulate neurons or neural tissue within a specific volume of tissue. In a preferred embodiment, the present invention includes a cannula, a plurality of leads, and at least one therapy delivery element or electrode at the distal ends of each of the leads. The cannula has a lumen and at least two openings at its distal end. The leads may be inserted into the cannula""s lumen and projected outward at the distal end from each of the openings along a predetermined trajectory. A therapy delivery device, such as a signal generator, is coupled to one or more therapy delivery elements, such as electrodes. The signal generator is capable of selectively providing electrical energy via the electrode to create an electrical field. The system may selectively adjust the electrical field created by the electrical energy. Optionally, a sensor may be included for generating a signal related to the extent of a physical condition for treating a neurological disorder or pain. The sensor signal may then be used to adjust at least one parameter of the electrical energy provided to the electrode.
In another embodiment, the present invention is implemented within a drug delivery system. In such a case, the therapy delivery device may be a pump and the therapy delivery element is a catheter. Alternatively, both electrical stimulation and drug delivery may be implemented.
By using the foregoing techniques, electrical stimulation and/or drug delivery may be adjusted and/or steered to a precise target within a volume of neural tissue to provide the desired treatment therapy. Further, the present invention provides a method of lead placement that allows the surgeon to explore a larger volume of brain tissue using only a single pass of the lead introducer into the brain which will reduce the inherent risk of surgery. Examples of the more important features of this invention have been broadly outlined above so that the detailed description that follows may be better understood and so that contributions which this invention provides to the art may be better appreciated. There are, of course, additional features of the invention which will be described herein and which will be included within the subject matter of the claims appended hereto.